The passion of flying has accompanied human beings from the early days of the humankind. The well-documented Helical Air Screw drawing of Leonardo Da Vinci in the fifteen-century was an important step towards a vertical take off, hovering and landing flying apparatus. It was only when a light weight powerful enough engine for powering rotating blades become available when Paul Cornu took off vertically in 1907. Vertical flights became easier and smoother when gyro control became available in mid-1940's and became common about a decade later.
A helicopter typically has two rotor blades that are connected through a drive shaft to an engine. The air deflected downwards due to the spinning of the rotor blades provides the lilting power. Rotor blades at the tail of the helicopter are directed in the horizontal plane to provide the anti-torque power that is required in order to prevent the helicopter from rotating due to the spinning main rotor. Changing the main rotor blades attack angle provides horizontal motion according to pilot's commands.
Sikorsky and Kamov first introduced a helicopter with two counter rotating main rotors on a common axis. Eliminating the need for tail rotor blades, the counter-rotating blades provide higher maneuverability and stability.
Flying toys history is even longer than that of flying vehicles. Unlike flying vehicles, flying toys are typically very price-sensitive. They should be stable, easy and safe to fly.
Consequently, Remote control flying toys should be designed to be inherently stable, with safe and durable structure and materials, using low cost components and very simple to manufacture.